(1) Field of the Invention
The present invention relates to a fiber optic transducer and more particularly to a small diameter bifurcated multi-lever miniature, fiber optic lever hydrophone having high sensitivity.
(2) Description of the Prior Art
The utilization of a bifurcated fiber optic bundle for the detection of minute mechanical displacements has been previously described in several U.S. patents. Kissinger, in U.S. Pat. Nos. 3,327,584 and 3,940,608 proposed the use of two optical fiber bundles joined randomly at one end to construct a fiber optic proximity probe while Frank, in U.S. Pat. No. 3,273,447 introduced a similar method for the detection of temperature, pressure and other quantities. This concept has also been applied to the measurement of pressures as described by Strack, in U.S. Pat. No. 3,580,082 and Porter in U.S. Pat. Nos. 3,789,667 and 4,210,029. Moreover, the concept has been extended to the monitoring of acoustic pressures and pressure gradients by Palmer in U.S. Pat. No. 4,310,905 and in my U.S. Pat. No. 3,831,137, respectively. With the exception of Palmer, the key element of the above fiber optic lever patents is a flexible bifurcated bundle of optical fibers whose common end is placed in the vicinity of a reflective surface such that any motion of the reflector modulates the light intensity of the reflected light beam entering the receive fibers thus generating an electrical signal proportional to the light variations. It is noted the the sensitivity of such a device is proportional to some light transfer coefficient, which can be expressed as the ratio of the optical power intercepted by a receiving fiber at the distal end upon reflection to the total light power emitted by a transmitting fiber at the same end. In addition, the sensitivity is proportional to the total number of adjacent transmit/receive fiber pairs used in the bundle. Thus, for good sensitivity the transmit/receive fiber distribution at the distal end must be maximized while the total number of fibers must be large thereby restricting the minimum possible size of a detecting probe. In some applications, such as in the implementation of the fiber optic lever towed array described in my co-pending U.S. patent application, Ser. No. 547,273, small probe dimensions are important. In addition, when the concept of the above application is extended to the log periodic array approach described in my U.S. Pat. No. 4,363,115 the upper frequency limit of operation is dependent upon the closest element spacing realizable with the smallest possible element design. What is required is a small diameter fiber optic lever probe with high sensitivity.